The present invention refers to a method of supplying fuel and air to an internal combustion engine. In the case of which fuel is supplied to at least one injection valve and combustion air is supplied to at least one intake pipe provided with a throttle.
Methods of supplying fuel and air to an internal combustion engine, in the case of which the internal combustion engine takes in combustion air through an intake pipe having provided therein a throttle, are already known. The throttle is in this case coupled to an accelerator pedal so that the degree of opening of the throttle determines the size of the free flow cross-section of the intake pipe and, consequently, the amount of air taken in. It follows that an acceleration or a deceleration of the speed of the internal combustion engine is controlled via the position of the throttle. In the case of the methods known, the amount of combustion air determined by the position of the throttle is measured, said amount of combustion air being then inputted into a separate control circuit as an input value. This control circuit then determines, in response to this input value, the amount of fuel which has to be supplied to the engine by means of an injection nozzle for the purpose of providing satisfactory operating conditions for the internal combustion engine. It follows that these known methods operate in response to the amount of combustion air taken in by the engine and control, in accordance with said amount of combustion air, the amount of fuel required. In the case of known devices for carrying out these methods an air-quantity measuring device is provided upstream of the respective throttle, said air-quantity measuring device being used for the purpose of determining the amount of air taken in by the engine. This air-quantity measuring device provides either a mechanical or an electrical correcting variable which is supplied to a suitable control means. Independently of the control means and independently of the throttle, a fuel pump applies a suitable fuel pressure to the fuel line provided upstream of the injection valve. This fuel pressure always has a constant value irrespectively of the operating conditions of the internal combustion engine. The control means cooperates with the injection valve in a mechanical or in an electronical manner and determines the opening time of said injection valve in response to the amount of air taken in. It follows that these known methods are based on the idea of controlling, in response to an engine operating parameter (amount of air taken in) a second operating parameter (amount of fuel required). Hence, the known devices for carrying out these methods always provide an air-quantity measurement which influences via the control means the opening time of an injection valve with the aid of which fuel having a constant pressure is injected. The fuel pump itself and the pressure of the fuel in the fuel line do, consequently, not participate directly in this method. These known methods show several serious disadvantages. The air-quantity measuring devices required for carrying out these methods are very complicated and susceptible to failure and do not permit any faultless measurement of the combustion air taken in, since fluctuations in the air temperature and influences exerted by varying flow conditions cannot be excluded. Primarily in the case of noload operation and in the case of maximum-speed operation of the internal combustion engine, an exact measurement of the amount of air and an appropriate apportioning of the amount of fuel is hardly possible. Furthermore, the inertia of the air-quantity measuring devices used exerts an influence on the reaction time of the control means and produces thus a quite substantial engine operating period, e.g. during acceleration or during throttling down, during which an undesirable ratio exists between the amount of fuel injected and the amount of combustion air taken in by the engine. The devices used for carrying out the known methods of supplying fuel and air to an internal combustion engine are, on the whole, very complicated, and this has the effect that not only the production costs but also the amount of maintenance work required is substantially increased.
Methods which are additionally known are methods of supplying fuel and air to an internal combustion engine in the case of which the combustion air has applied thereto an appropriate pressure by means of a compressor or a blower. However, said blowers or compressors either operate such that they are completely independent of the speed of the internal combustion engine or they are directly connected to the crankshaft of the internal combustion engine so that they produce a specific air pressure in the intake pipe, said air pressure being not consistent with the amount of air taken in by the internal combustion engine. It follows that, in this case, too, it will be necessary to control the amount of air, which is to be supplied to the internal combustion engine, by means of a throttle coupled to an accelerator pedal. In the case of these methods the measurement and control processed required for determining and for injecting the necessary amount of fuel are very complicated and susceptible to failure. In particular, in the case of the devices on which these methods are based, the measure of supplying the fuel under pressure to a fuel line by means of a separate fuel pump cannot be dispensed with either. Hence, these devices are provided with two separate pumps, one for the fuel and one for the combustion air. The mode of operation of these two pumps cannot be coordinated so as to obtain a desired ratio between the combustion air and the fuel.